Flanked on all sides by beautiful women, Mutassim Gadhafi, son of embattled Libyan leader Moammar Gadhafi, sat in a crisp white shirt with his hair slicked back and quietly sipped expensive champagne straight from the bottle on a lush Caribbean island while Beyonce serenaded him on New Year's Eve 2009.

Mutassim looked perfectly at home amid luxury and celebrity -- a man who seemed "accustomed to that kind of life," Tom Groves, one of the lucky few invited to the bash, told ABC News.

If Mutassim was in his element, it may be because the reportedly million-dollar bash was a repeat of the same party he threw exactly a year earlier at the same St. Barts nightclub, except with a different diva on the mike. On New Year's Eve 2008, Mariah Carey provided the entertainment, according to a leaked U.S. State Department cable that described Mutassim's island bashes in detail. That cable, along with several others posted on the website Wikileaks, also tagged Mutassim and several of his seven brothers as "hard-partying" and "womanizing" playboys.

Video shot by Groves, which was obtained by ABC News, shows an intimate affair with Beyonce singing several songs just feet away from party-goers. In other videos of the party posted on YouTube, celebrities Jay-Z and Usher are seen together ringing in the New Year. Groves said among the 150 attendees were other A-listers like Jon Bon Jovi and Lindsay Lohan -- all treated to Cristal champagne.

Despite the heavy celebrity attendance, "Mutassim seemed to be surprised by the fact that his [2010] party was photographed and the focus of international media attention," a U.S. official said in a 2010 cable. "His carousing and extravagance angered some [Libyan] locals, who viewed his activities as impious and embarrassing to the nation."

Representatives for Beyonce, Usher, Mariah Carey and Lindsay Lohan did not respond to requests for comment on this story.

CLICK HERE to read about leaked U.S. diplomatic cables on Gadhafi himself.

Cable: 'Only a Matter of Time' Before Another Gadhafi Son Gets in Trouble

But if the lavish soiree was embarrassing to some, some other international news coverage the family received just a few days before was worse. Then, one of Mutassim's seven brothers, Hannibal, allegedly physically abused his wife, who was later told to tell investigators she had been injured in an "accident," a U.S. official said in a leaked cable.

Hannibal and another brother, Saadi, have "checkered histories of unseemly behavior and public scuffles with authorities in Europe and elsewhere," the official said. According to the same document, another of Gadhafi's sons, Saif al-Arab, described as a "ne'er-do-well," lives in Munich where he "pursues ill-defined business interests and spends much time partying."

"The German Ambassador has expressed concern to us that it is only a matter of time before there is an incident involving him," the official said.

Some of Gadhafi's sons brought so much negative attention to the family that the Libyan dictator assigned a high government official to play the role of a "minder of the more troublesome [Gadhafi] offspring," according to the documents. After an incident in which Saadi disobeyed his father's orders and traveled to Rome, Italy, that minder was removed and Gadhafi's daughter, Aisha, reportedly filled the void.

The Wikileaks disclosures are not news, however, to the Libyan people, who have been well aware of the exploits of the Gadhafi children for years, according to Mansour El-Kikhia, chairman of the department of political science and geography at the University of Texas at San Antonio and author of "Libya's Qaddafi: The Politics of Contradiction".

"We have been talking about what they do, how spoiled they are, how much they abuse their position, how much they manipulated the system to serve themselves," El-Kikhia told ABC News.

Beyond the Parties, Reaching for Power

Behind the tabloid escapades, however, other leaked cables show an intense game of political maneuvering between the brothers -- especially Mutassim and Saif al-Islam -- over who would succeed 62-year-old Moammar Gadhafi.

It was Mutassim that requested $1.2 billion directly from the chairman of Libya's National Oil Corporation so he could "establish a military/security unit" to rival the one run by his younger brother, Khamis, a 2009 cable said.

Mutassim was also the one greeted warmly the same year by U.S. Secretary of State Hillary Clinton in Washington, D.C. With Mutassim at her side, Clinton told reporters at the time she was "very much looking forward" to broadening and strengthening the relationship between the two nations.

But Saif al-Islam had managed to win over many Libyans, one cable noted, by staying relatively clear of the public debauchery and publicly calling for reform -- even by occasionally sharply criticizing his father.

In 2007, Saif al-Islam publicly confirmed for the first time the torture of six Bulgarians who were held in Libya for several years which had been reported by several international news organizations.

In a speech the next year, Saif al-Islam criticized the "forest of dictatorships" in the Middle East and called for a "more robust civil society, judicial reforms, greater respect for human rights and more press freedoms," one cable said.